Optical coherence tomography (OCT) can acquire a tomographic image of a sample with high resolution and is mainly used as an ophthalmic instrument. An apparatus using the OCT (OCT apparatus) is equipped with a coherence system and can conduct measurement with high sensitivity by irradiating an eyeground with a measuring beam (low coherent beam) and combining a return beam from the eyeground with a reference beam. At this time, the measuring beam is projected at a predetermined position of the retina to acquire a tomographic image of the eyeground.
Here, it may be difficult in some cases to project the measuring beam at the predetermined position of the retina due to factors of eyes to be inspected, such as amblyopia. At this time, it is necessary to project the measuring beam at the predetermined position of the retina by adjusting an optical system according to the optical characteristics of each eye to be inspected, and so it takes a long time to adjust the optical system.
In recent years, there has been a stronger demand for acquiring a tomographic image with high resolution by the OCT apparatus. Therefore, when a tomographic image is acquired by making a beam diameter of a measuring beam large, it takes a longer time to adjust such an optical system.
On the other hand, it is also desired to shorten the time for adjusting the optical system. In particular, shortening of the time required of imaging in the ophthalmic diagnosis of the retina is related to lightening a burden on a subject, so that it is strongly desired to shorten the time for adjusting such an optical system.
In order to meet the above two demands, an optical apparatus using OCT and optical coherence microscopy (OCM) is disclosed in Japanese Patent Application Laid-Open No. 2002-174769 (Patent Art. 1). This apparatus is so constructed that OCT is used in confirmation of a large structure in a vital sample and can be changed to OCM when a noticeable region therein is observed with minuter resolution. At this time, OCT and OCM are greatly different in depth of focus, so that the apparatus is so constructed that beam diameters can be set according to OCT having a small numerical aperture and OCM having a great numerical aperture using a beam diameter converting optical system to permit observation at a high S/N ratio.